This invention relates to an apparatus for detecting the position and inclination of a fine object.
When an integrated circuit (IC) pellet is bonded on a bonding base, it is necessary to detect the position and inclination of the IC pellet. To detect the position and inclination of an IC pellet, at least two position marks are usually provided on the pellet at different positions. Then, a television camera forms an image of the IC pellet. Based on the image signals from the television camera there are obtained the coordinate of each position mark. According to the coordinates of the position marks thus obtained, the position and angle of inclination are detected.
As apparatus which detects the position and inclination of a fine object in such a manner as mentioned above is disclosed in U.S. Pat. No. 3,603,728. But in some cases such conventional apparatus fails to perform its function for the following reason.
To focus an enlarged image of an IC pellet on the photosensitive surface of a television camera, a magnifier should be used. In this case, the magnification of the magnifier is selected so that the two position marks fall within the scanning region of the photosensitive surface of the television camera. Thus, if the two position marks are provided on the opposite edge portions of the IC pellet for some reason, the magnification of the magnifier should inevitably be lowered. Otherwise, both position marks would not fall within the limited scanning region. As a result, the image of the IC pellet obtained becomes small, and the position marks look very small, too. Thus, when such small position marks are scanned, no image signals having a large amplitude can be obtained. Consequently, desirable signals which represent the position of the IC pellet cannot be obtained, and the position of the IC pellet cannot be accurately detected.
To eliminate the above-mentioned drawbacks, the position marks may be made broader or larger. However, an IC pellet is so small and the circuit pattern on it is so dense that the position marks can hardly be made larger. Instead, the television camera and the magnifier may be moved together, or only the magnifier is moved, thereby to magnify much more one position mark at a time. This method, however, not only requires a very complicated apparatus but also is impracticable since it is very difficult to move and stop the television camera and/or the magnifier precisely at the right position. Further, this method requires much time to detect the position of the IC pellet, due to the necessary movements of mechanical devices. Thus, it is impossible with this method to carry out IC pellet bonding efficiently.